1. Field of the Invention.
The present invention relates to magnetic recording systems, and in particular to a recording system and method which utilizes buried servos for achieving high track densities, accurate track following operation, and constant linear density in spite of speed variations of the magnetic recording medium.
2. The Prior Art.
It has long been an objective in the magnetic recording technology to provide a system that permits recording of information on a magnetic medium in high track densities, and with high lineal densities One way by which the track density may be improved is to provide a system and a method for accurately following the tracks Higher lineal densities may be achieved by reducing the amount of control information needed to be stored in the information storage area of the magnetic medium.
One technique for providing higher track and lineal densities involves the use of a servo signal, i.e., a track-location indicating signal, which is superposed with a data signal, in the magnetic medium This technique is utilized in the system disclosed in U.S. Pat. No. 3,404,392 to Sordello. The Sordello patent teaches use of a dual layer magnetic coating on a disk substrate. A lower layer has a higher retentivity and coercivity than an upper layer. A servo signal is first recorded in the lower layer for indicating track position Following such recording, data signals are recorded in the upper layer Then both the servo and data signals are sensed. This dual layer configuration allows the servo signals to remain undisturbed by subsequent writing and rewriting of data signals in the upper layer. There are no recording operations disclosed which are based upon sensing the servo signals.
For each data recording operation in the Sordello reference, an erase gap precedes a read/write gap so that the data signal can be successfully recorded in the upper layer. During read-back, not only is the data signal read back by a single gap, but two sets of servo signals also are simultaneously read back Sordello utilizes linearly recorded sine waves that are written in concentric circular tracks, with adjacent servo tracks being written at different frequencies. Each data track is superposed over 1/2 of an odd numbered servo track, and over 1/2 of an even numbered servo track The data signals are recorded at a high frequency, which is at least three or four times the frequency of the servo signals in the lower layer, thereby enabling the data signals to be separated from the servo signals by filtering. The Sordello recorder uses a single gap or transducer for simultaneously reading the control or servo signals along with the data signals. The filtered servo signals are used to accomplish alignment of the Sordello transducer on the tracks of the magnetic medium.
Subsequent developments have attempted to improve on the Sordello system by providing structure such as first and second transducers, which are arranged in the longitudinal direction of a record track One of the transducers is used for reading or writing data onto the magnetic medium The other transducer is used for reading the servo control signal, which is prerecorded in the high coercivity portion of the magnetic medium The information from the transducers is passed to a filtering system for, in one case, identifying the position control signals in order to appropriately position the transducers in the tracks. In another case, the filtering accomplishes separation of the information stored on the magnetic medium from the servo control signals, so that the information or data may be retrieved and passed to output devices, or used for other purposes.
Systems such as those described above have resulted in an increase in track density recording However, these systems continue to be unduly cumbersome since they require additional circuitry for separating and segregating the data signals from the servo signals, which separation and segregation is necessary for substantially any practical utilization of the system. In addition, these systems include a clocking system that typically requires an extensive amount of clocking data to be included in the data layer of the magnetic medium, in order to synchronize the reading operation with the speed of the magnetic medium as it passes adjacent the transducers of the system. Clocking schemes requiring large percentages of the data-layer storage space for this clocking data continue to be used in current systems.
As is apparent from the above discussion, what is needed in the art is a system and method for recording data signals in a magnetic medium that provides accurate track alignment in order to permit high track density, and that also provides for a minimum amount of clocking information to be stored within the data signal, so as to permit accurate, high level, lineal data storage density. It would be a further improvement in the art to provide such a system that provides improved linear recording accuracy by accurately eliminating the effects of media speed variations on linear recording density. A still further improvement in the art would be to provide a system and method whereby the servo control signals and the data signals could be retrieved from the magnetic medium independently of one another and without the use of filtering arrangements for accomplishing this purpose. Such a system and method is described and claimed herein.